This invention relates to adjustable pliers and, more particularly, to precision pliers which provide precise self-locking engagement and automatic adjustment of jaw spacing for engagement of an object.
Various self-adjusting and self-locking tools have been heretofore known, for clamping, gripping, or otherwise providing adjusting of jaw configuration upon engaging an object such as a workpiece or fastening element. A matter of importance in the design of such tools is to provide a tool construction and design which provides easy, quick, reliable, and precise operation. If pliers are to be provided with self-adjusting jaws, there must be a mechanism for reliably and positively causing the jaws to cease their adjusting movement upon engagement of an object and to retain such position reliably so long as the pressure is maintained upon the tool by the user. In one type of construction, such as disclosed in U.S. Pat. No. 4,651,598, a pawl member is intended to provide interengagement of jaw portions by movement within a channel, one side of the channel defining a raceway and the other having a series of teeth to be engaged by the pawl. The pawl is formed with a pointed tip which, upon engagement of a workpiece by the jaw, is caused to engage one of the teeth. The pawl tip when so engaged is exposed to high compression and shear forces, such as to present the risk of its fracture and to heighten the potential for wear upon its surfaces and the teeth during use. These factors present potential either for compression or shear failure when extreme pressure is applied to the tool by a strong user or for slip failure in which the pawl tip slips from one tooth to the next. Therefore, it has previously been proposed to use multiple pawl teeth in self-adjusting pliers.
An additional aspect of concern in the design is for the tool to provide a desirable "feel," that is, tactile feedback through the user's hand when engaging an object. A pawl with single tip or tooth engagement as provided in the above-identified patent, provides only a limited adjustment due to the pitch of the teeth, which is large as a result of the single tip on the pawl. The geometry dictates that the number of teeth available for engagement is relatively limited so that, when tip engagement finally occurs, the handles of the tool may not be angularly spaced for comfort and to permit maximum application of force by the user's hand.
There are some situations of use where self-adjusting pliers have not satisfactorily operated because the pawl did not always reliably engage, e.g., when the tool is inverted (as when used underneath the work as is common in vehicle repair work), where gravity might tend to prevent pawl teeth engagement. Also, the tool is susceptible to lack of pawl engagement due to differing hand grip forces. In general, self-adjusting pliers of the prior art have had no satisfactory means for ensuring controlled pawl engagement. Prior designs have used extra springs for exerting forces on a control arm in such pliers, but this is more complicated, less reliable and more expensive.
A significant concern in the design of self-adjusting, self-locking pliers is to be able to manufacture the pliers economically. Heretofore, designs for self-adjusting pliers have not been suited for being manufactured by the use of forged, single-piece elements. Thus, it has been proposed variously to use laminated, riveted handle pieces, clamshell handle elements, and other unsatisfactory constructions for enclosing various springs. Handle designs in such prior art tools are not commercially satisfactory, and their inability to use forgings compromises not only cost but deprives the tool of the inherent strength of forgings.
Accordingly, among the several objects of the invention may be noted the provision of an adjustable pliers which provides precise automatic jaw adjustment to permit one-handed operation by the user with reliable self-looking establishment of jaw position upon engaging an object with slip-free engagement of an object providing optimum angular spacing between its handles; which includes a precision locking pawl which establishes a jaw relationship upon gripping of an object with positive locking engagement of the jaws, in which multiple teeth of the pawl positively engage multiple teeth of a rack carried by one jaw-defining member; which includes means for ensuring controlled pawl engagement of the rack teeth, so as to ensure pawl engagement upon the jaws contacting an object under all conditions of use; which provides superior "feel" by tactile feedback to the hand of the user upon gripping engagement of an object in its jaws; which is inherently resistant to wear by reducing the contact pressure of the pawl teeth with those of the rack so as not only to avoid wear but also to avoid change in dimensional relationships which otherwise may sacrifice reliability and long life of the pliers; which permits the use of one piece forged handle-defining members for strength and economy; which provides a superior handle configuration permitting maximization of the gripping force by one-handed operation of the user; and which is easily and economically manufactured with high, repeatable degree of precision.